These are the steps that I have taken, and at the moment the editor opens and works.
After doing all that's mentioned above and failing to make the editor work, I went to my Steam Library, right clicked on Football Manager 2023, A menu appears, I clicked on Properties, then Local Files, Revalidate (or something to that effect). As I said, it's now working. I hope this works for you too. Thanks to @metal_guitarist for the pointer.